Prior attempts to make diving masks are best represented in U.S. Pat. No. 3,055,256 issued Sep. 25, 1962 to John H. Andreson, Jr., U.S. Pat. No. 3,672,750, issued Jun. 27, 1972 to Kenneth G. Hagen and U.S. Pat. No. 3,320,018 issued May 16, 1967 to Max H. Pepke. The Andreson U.S. Pat. No. '256 patent discloses a mask for divers with imperfect vision which includes a conventional mask frame in which is mounted a spherical lens, conventionally aligned.. The Hagen U.S. Pat. No. '750 patent discloses a diving mask with curved lenses for each eye, with a centre of curvature for each lens at the eyeball of the user. The Hagen mask should be custom made for each category of user to locate the specific eye points (e.g. optical centres and eye depth) properly; a universally acceptable mask cannot be made according to the teachings of Hagen. Further, it has been found that only slight shifting of the Hagen mask on the user's face distorts one's vision to such an extent that nausea may result. For this reason, then, such a diving mask is fundamentally unacceptable.
Pepke U.S. Pat. No. '018 is relevant at FIG. 20, showing a diving mask, again with spherical lenses having separate centres of curvature but located at the pupils of the eyes of the user, rather than at the centres of the eyeballs. The Pepke mask suffers the same deficiencies as Hagen's; the teachings of the Pepke patent cannot be used to produce a universally acceptable, distortionless vision mask but only individual masks, custom made for each category of diver user.
Remaining prior art disclosures are remote. U.S. Pat. Nos. 2,876,766 issued Mar. 10, 1959 to Dimitri Rebikoff et al and U.S. Pat. No. 3,010,108 issued Nov. 28, 1961 to Melvin H. Sachs illustrate diving mask lenses curved laterally and vertically. However, neither patent even remotely suggests a mask lens curvature specifically designed and configured to provide distortionless vision underwater. The distortions inherent in such unspecified curvatures have also been found to dangerously cause nausea to users. U.S. Pat. Nos. 2,952,853 issued Sep. 20, 1960 to Howard A. Benzel and U.S. Pat. No. 3,027,562 issued Apr. 3, 1962 to James K. Widenor are more remote and simply show diving masks curved in a single plane only; vision distortion is only exacerbated by such a construction, not alleviated. U.S. Pat. No. 3,483,569 issued to Israel Armendariz is similar. Again, the safety-threatening condition of diver nausea is inherent in these designs.
More exotic disclosures of attempts to provide magnification-free underwater vision are provided by U.S. Pat. Nos. 3,040,616, issued Jun. 26, 1962 to George R. Simpson and U.S. Pat. No. 4,373,788 issued Feb. 15, 1983 to M. Linton Herbert. These patents disclose dual `focal point` lenses structures with air chambers behind the lenses in the former patent and a filling and draining bladder structure in the latter to permit readjustment of several lenses. Clearly, both designs are unfavourably complex and impractical.
Other prior art disclosures directed to attempt to improve certain aspects of underwater vision and/or provide diving mask myopia-correction lenses include U.S. Pat. Nos. 2,928,097 issued Mar. 15, 1960 to Lester N. Neufeld, U.S. Pat. No. 3,051,957 issued Sep. 4, 1962 to Chester C. Chan and French Patent No. 1,374,010 issued Aug. 24, 1964 to Jean-Louis Marro and an article entitled "Visual Problems of Skin Diving" by James R. Gregg, Skin Diver Magazine, April 1961, reprinted in The Optometric Weekly, Jul. 13, 1961, pp. 1381-1388.
What the prior art fails to disclose is a diving mask having a lens configured to provide substantially distortion free underwater vision, a major portion of the mask lens being curved so that the apparent magnification of images underwater is less than that observed through a conventional, flat lens plate, certain portions of the lens being further curved to eliminate or mitigate pincushion-type distortion. Further, the prior art also fails to disclose an improved application for a simple spherical mask lens which is incorporated into a skirt narrow enough to allow the user's nose to extend forwardly of the lens and whereby the optical axis is tilted in a forward vertical plane.